Rehabilitation engineering aims to improve the quality of life for individuals with varying disabilities. Paraplegia, for example, has seen significant attention from the rehabilitation field, offering several mobility devices, orthoses, and accessories to improve the client's independence. Other disabilities, especially those, which have a variety of forms or progress very quickly, have seen little attention. Muscular Dystrophy (MD) is this type of disability. Muscular dystrophy is a genetic, degenerative disease, which destroys muscle tissue leading to decreased mobility and independence.
Muscular dystrophy is a term used to describe any one of a group of degenerative muscular diseases. MD causes weakness or wasting away of the skeletal muscles. There are over 40 identified neuromuscular diseases. They are hereditary and express themselves in known patterns of inheritance. The diseases are myopathies because they are an inherent disorder of the muscle. They affect all populations with no variation among regions.
Muscular dystrophies are a relatively rare condition. The most prevalent type, Duchenne, occurs in only 30 cases per 100,000 births. It was not until 1987 when scientists discovered the specific DNA alterations and could determine the exact protein that is missing or dysfunctional in patients with the disease. Prior to that date, doctors identified these diseases based on clinical and genetic characteristics. Currently, the differentiation between each type of muscular dystrophy is determined partially based on the pattern of inheritance and the affected muscle group(s).
Duchenne, the most common form of MD is inherited as an X-linked recessive disease. Therefore, this pattern generally affects males. Women are responsible for carrying the gene, but only in very rare cases ever experience any symptoms of the disability. Symptoms typically begin before the age of three with difficulty in walking. By adolescence, patients become confined in wheelchairs. Dexterity in the fingers and wrist remain high through the natural progression of the disease. Eventually DMD affects the respiratory muscles causing death.
A rehabilitation device, which would increase the range of motion of muscle groups, would benefit clients suffering from Duchenne's MD by improving their independence and overall quality of life. Such a product could have influence in the rehabilitation, therapeutic, and medical markets for clients with afflictions other than muscular dystrophy. The potential exists for the product to also aid patients with arm tremor and tendonitis, to rehabilitate those suffering from stroke and arthritis, and to assist in therapy for those recovering from surgery or injury.
The human body is composed of some of the most intricate and ingenious mechanical systems known to man. The arm, specifically, involves a precisely arranged set of muscles and joints, which allows a person to target any object within his/her arm's radius. In total, the arm incorporates seven degrees of freedom (DOF) to complete its specified motions. These DOF occur at joints of the shoulder, elbow, and wrist regions by multiple movements at each joint. The shoulder joint allows the arm to swing forward and backward (forward flexion and backward extension), swing laterally (horizontal flexion and horizontal extension), and swing about an axis through the front of the body (abduction and adduction). The wrist joint allows the hand to swing up and down (flexion and extension) and swing sideways (radial deviation and ulnar deviation). The elbow joint accounts for the remainder of the arm's DOF with its forearm pronation and supination (rotation of the forearm and wrist about an axis through the forearm) and its elbow flexion and extension (a curling motion between the forearm and upper arm).
The skeletal structure 10 of the arms and upper torso is shown in the front and rear views, respectively of FIGS. 1A and 1B. The humerus 11 is the solitary bone in the upper arm's skeletal structure. This bone pivots in three rotational DOF from its proximal end at the shoulder joint 12, the way a rod pivots with its end connected to a socket as a ball joint. The connection of the humerus 11 to the joint occurs at the scapula 13 and the clavicle 14 at the shoulder, and the scapula's glenoid cavity serves as the socket joint in this connection. The motions that this joint allows include the abduction, flexion, and extension as well as humeral rotation. Humeral rotation is associated with the motion of forward flexion and backward extension. As one extends an arm forward, the arm rotates orthogonally about an axis 15 through the side of the shoulder. When the arm abducts to 90 degrees, the person can still make a rotation about the arm by rotating the humerus 11. The DOF of rotation about the arm can be achieved at different positions. The distal end of humerus 11 connects to the elbow joint 16, where it is the base for the flexion and extension of the forearm. The ulna 17 and radius 18 are the two bones that comprise the skeletal structure of the forearm 19. The ulna 17 serves as an axis about which the radius 18 can revolve, in order to produce the pronation and supination of the wrist 20. The proximal end of the forearm 19 attaches to the elbow joint 16, where it acts as a lever with respect to the humerus 11. The distal end of the forearm 19 connects to the hand with an intricate array of muscles, bones, and ligaments.
In view of the above discussion, it would be beneficial to have a powered arm orthosis capable of manipulating a disabled arm in the normal manner of common arm movements such as humeral rotation and elbow flexion.